题目

第三部分：阅读理解（共20小题，每题2分，满分40分） 请认真阅读下列短文，从短文后各题所给的四个选项（A、B、C和D）中，选出最佳选项,并在答题卡上将该项涂黑。 The story is about a 92-year-old lady. She is fully dressed each morning by eight, with her hair fashionably done and makeup perfectly applied. She is moving to a nursing home today. Her husband recently passed away, making the move necessary.       After waiting for many hours patiently in the lobby（大厅） of the nursing home, she smiled sweetly when told her room 为研究某种材料的荧光特性，兴趣小组的同学设计了图示装置，让质子经过MN两金属板之间的电场加速后，进入有界匀强磁场，磁场的宽度L=0．25m．磁感应强度大小B=0．01T，以出射小孔O为原点，水平向右建立x轴，在0．4 m≤x≤0．6 m区域的荧光屏上涂有荧光材料，（已知质子的质量m=1．6×10-27kg，电量q=1．6×10-19C，进入电场时的初速度可以忽略）（1）要使质子能打在荧光屏上，加速电压的最小值是多少？（2）当质子打中荧光屏时的动能超过288eV，可使荧光材料发光。对于不同的加速电压，荧光屏上能够发光的区域长度是多少？